This study investigates the dynamics of soil loss and sediment export associated with land use/land cover changes and identifies soil loss hotspot areas in the Winike River basin of the Omo-Gibe basin of Ethiopia. Despite the substantial contributions of previous studies, research integrating estimates of soil loss and sediment export and their spatial variation associated with LU/LC change over space and time is still insufficient in Ethiopia (Sadeghi et al., 2008). Reductions in C and P factors are often reported to have increased soil loss and sediment export and are associated with greater loss of ecosystem regulatory functions (Durigon et al., 2014).
The InVEST model takes a compressive approach by analyzing the soil loss and sediment export at the outlet of the watershed from each land use type over a period of time. Aga et al., (2019) reported a loss of 2% of the designed storage volume of reservoirs each year due to sedimentation. The unique feature of the InVEST SDR model is its ability to analyze soil loss and sediment export from each type of land use and quantify the amount of sediment connected to the water bodies, including streams and reservoirs.
The parameters Borselli k (kb) and Borselli ICo (ICo and ICi) are calibration parameters that determine the shape of the SDR-IC relationship (Sharp et al., 2016). The performance of the model was verified using the residual root mean square (RRMSE), coefficient of determination (R2) and percentage bias average error (PBIAS) (Gyamfi et al., 2016; Munoth and Goyal, 2019). This indicates the suitability of the SDR model for simulating sediment loss and sediment export in the Winike Basin.
Frequent disturbance of the soil in cultivated land contributes to uncertainty in the estimation of sediment export when related to bare soil.
Discussion
Furthermore, soil loss and sediment export in the sub-basins varied significantly with elevation (P<0.01). This indicates that additional soil and water conservation practices (SWC) are needed in the upstream catchment. Farmers clear natural forests, shrubs and grasslands with the support of government agricultural extension services that provide seed and fertilizer to boost agricultural production (Aneseyee et al., 2019).
Therefore, the scenario analysis shows that from 2008 to 2018 there was a stronger land change, which worsened the soil loss and sediment export in the considered area. Such threats are also reported elsewhere in Ethiopia, suggesting that accelerated soil erosion in watersheds has resulted in dam silting (Getahun et al., 2013; Karki et al., 2018). Total soil loss and sediment export within the study area increased by 176.35 thousand tons and 3.85 thousand tons, respectively, in the last three decades (1988 to 2018).
Such parameter uncertainties were reported in many other studies (Merritt et al., 2003; Wang et al., 2001). With the land conversion from forest to cultivated land, loss of soil organic matter (SOM), which is the soil's aggregating agent; higher K values are linked to soils with lower SOM (Kodesova et al., 2009). Soil organic matter lowers K values because it can bind soil particles together and increases cohesion by reducing the loosening effect of raindrops, therefore reducing runoff and increasing infiltration (Hassen and Assen, 2018; Renard et al., 1997; Wischmeier and Smith , 1978).
In contrast, cultivated fields have the highest C values, as reported by Hamel et al. 2017) suggesting that these fields are sensitive to erosion hazards. The LU/LC change results in a degradation of soil resources that impacts climate change through biomass burning, deforestation, and depletion of soil organic carbon (Pacheco et al., 2018). In the study, rain-fed agriculture in watersheds is the most sensitive sector to climate change due to the fluctuations in rainfall (late and early rainfall).
This is one of the reasons for increasing cultivated land and decreasing vegetation cover, exacerbating soil loss in the study watershed. In recent years, the government of Ethiopia has implemented extensive land and water conservation measures through community-led watershed management and initiatives such as Productive Safety Net Programs (PSNP), community mobilization through free labor days, and the Sustainable Land Management Project (SLM) (Haregeweyn et al., 2015). These mass movements of Groundwater Conservation (SWC) highlights significant progress in land management practices in the study area.
Conclusion
However, to achieve sustainable conservation of ecosystem services, continuous maintenance of structures and continuous application of a scientific methodology is necessary. Therefore, the findings suggest the need for more conservation practices in the highly vulnerable sub-basin and a reduction in continuous cultivation in the higher elevation areas of the watershed to overcome the challenges of dam silting and ecosystem degradation in the lower part of the watershed. catchment. The research findings also suggest that policy instruments should be implemented by creating a buffer zone and implementing urgent conservation activities in the sub-basin of the study area to prevent soil loss and sediment export in downslope dams.
Furthermore, study on evolution of the soil fertility over time, associated with LVE/GK and soil erosion is one of the future recommended research areas in this watershed. Funding: This research work was supported by CASACPE project; branch office of Hawassa, Ethiopia and Addis Ababa University thematic research project. Acknowledgments: We would like to thank Wolkite Soil Laboratory for performing the soil analysis and the Center for Environmental Science at Addis Ababa University for providing financial support.
The authors thank the native English speaker and experienced researchers for linguistic support. Finally, the authors would also like to thank the editor and the anonymous reviewers for their comments, which greatly improved the scientific quality of this work.
Hydrodynamics of topographically confined lakes in the Ethio-Kenya rift: the case of Lakes Awassa and Naivasha. Soil Erosion Hazard Assessment and Prioritization for Treatment at Catchment Level: A Case Study in the Chemoga Catchment, Blue Nile Basin, Ethiopia. Impact of land-use change on water-related ecosystem services: a study of the Guishui River Basin, Beijing, China.
Comprehensive Soil Erosion Risk Assessment for Better Land Use Planning in River Basins: Case Study of the Upper Blue Nile River. The consequences of changes in population, land use and land management for surface runoff in Ethiopia's Upper Nile Basin. Analysis of land use/land cover change using object-based classification approach in the Munessa-Shashemene landscape of the Ethiopian highlands.
Geospatial assessment of vulnerability to soil erosion in the upper uMgeni catchment in KwaZulu Natal, South Africa. Land use/land cover changes and their environmental impacts in the Gelana sub-basin of the Northern Highlands of Ethiopia. Impacts of land use change due to land use on runoff and sediment yield of the Upper Tapi River sub-basin, India.
Impact of Land Use Changes in Land Use on the Risk of Soil Erosion: The Case of Denki River Catchment in Ankober Woreda, Addis Ababa University. Governing green industrialization in Africa: assessing key parameters for a sustainable socio-technical transition in the context of Ethiopia. Land use and land cover changes and soil erosion in the Yezat River Basin, Northwestern Ethiopia.
34;The Nature and Causes of Soil Degradation in the Oromiya Region, Ethiopia-A Review." International Livestock Research Institute. 34;Temporal Changes in Biomass Production, Soil Properties and Soil Flora in Eucalyptus globulus Plantations in the Central Highlands of Ethiopia.". Determining the Effects of Land Use Change on Sediment Export: Integrating Sediment Source and Sediment Delivery in the Qiantang River Basin, China.
In the study area, livestock is abundant and pasture is the main source of fodder for cows, goats, sheep, horses and donkeys. In the summer season, starting from June to September (duration) sufficient amount of grass is available for the animals, but the remaining months (October to May) become dry season and cause fodder shortage. In this dry season, grass and some perennial vegetation remain dormant, but cattle use the same grazing land year after year, which can cause soil erosion.
The changes in land use/land cover greatly affect soil erosion and sediment export dynamics.
